Compressor Design

The five basic refrigeration compressor designs are described below and compared in Table 37-1:

• Rotary compressors have an out-of-center rotor that rotates within a cylinder. Applied designs include use of a rolling piston or sliding vanes.

• Scroll compressors have two spiral-shaped parts; one remains fixed while the other orbits against it. Suction gas is brought in from the outer portion and

Characteristic

Rotary

scroll

Reciprocating

screw

Capacity Range

< 5 tons (< 18 kWr)

5-10 tons (18-35 kWr)

< 1-150 tons (< 1-525 kWr)

100-750 tons (350-2,600 kWr)

100-10,000 tons (350-35,000 kWr)

Maximum Capacity Range

5 tons (18 kWr)

10 tons (35 kWr)

400 tons (1,400 kWr)

2,000 tons (7,000 kWr)

20,000 tons (70,000 kWr)

Types

Sliding vane, rolling piston types, welded shell only

Compliant and non-compliant, welded shell only

Open, serviceable, and welded shell hermetics

Rolling rotor open and hermetic

Single and multi-stage open and hermetic

Displacement

Positive

Positive

Positive

Positive

Not positive

Capacity Control

Variable speed and on-off

Variable speed and on-off

Variable speed, on-off, and cylinder unload

Variable speed and intake slide valve

Variable speed and guide vanes

Table 37-1 Comparison of Currently Applied Compressor Technologies.

Table 37-1 Comparison of Currently Applied Compressor Technologies.

compressed gas exits at the center of the scrolls.

• Reciprocating compressors have a piston(s) that travels back and forth in a cylinder(s).

• Screw compressors have two helical rotors, one male and the other female. As they turn, the rotors mesh.

• Centrifugal compressors have a high-speed impeller with numerous blades that rotate.

Rotary compressors are commonly used in appliances such as refrigerators or water coolers and for air conditioning and heat pump units of less than 5 tons (18 kWQ. The scroll compressor is typically used in applications of about 5 or 10 tons (18 to 35 kWQ. The three major compressor types, however, are the reciprocating, screw, and centrifugal, which are used for almost all larger-capacity applications. These three types, which are discussed in detail below, may be designed as single- or multiple-stage units, depending on the application requirements.

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